Yes, I'm totally sure! In the Russian, they respell the foreign non-Russian non-cyrillic lettered words with cyrillic letters. This word "Nagant" have to pronunce -> "Nagan" (in several language), like his compatriot name: "Poirot" (have to pronunce -> "Poaro")
(Both men (would) were Belgian )
...so in German that word - Nagant - have to write: "Nagant" ...

Yes, I'm totally sure! In the Russian, they respell the foreign non-Russian non-cyrillic lettered words with cyrillic letters. This word "Nagant" have to pronunce -> "Nagan" (in several language), like his compatriot name: "Poirot" (have to pronunce -> "Poaro")
(Both men (would) were Belgian )
...so in German that word - Nagant - have to write: "Nagant" ...